i wouldnt touch the water pump unless it shows cause for concern
deffo as above aux belt/tensioner,big failure point
will be obvious if its a new belt once you get top cover off[remove engine mount and cover-15 mins or so]
if you go that far pop a new belt on,its only about another 40 mins work...
it cost me under £100 for volvo cambelt,tensioner,roller and 4 nuts/1 big nut
another £60 or so for tensioner/aux belt and £25 for volvo stretch a/c belt[which i kept as spare as mine was just changed anyway